This invention relates to a service and emergency braking system for an articulated vehicle having service brakes actuated by air pressure and also having emergency brakes which are held in their released condition by air pressure.
Articulated vehicles of the type which have air actuated brakes are normally provided with a trailer control line interconnecting the two portions of the vehicle for communicating service brake control pressure from the tractor to the trailer brakes and are also provided with a trailer supply line to provide actuation pressure for the trailer service brakes and pressure for operation and control of the trailer emergency and/or parking brakes. Prior art braking systems for these vehicles have provided a tractor protection system which does apply the trailer emergency brakes and also shuts off communication through the lines interconnecting the tractor and trailer portion of the vehicle, when the fluid pressure level in the tractor braking system has been depleted to a predetermined low level. Although these systems function satisfactorily, in a situation in which the trailer control line interconnecting the tractor portion of the vehicle with the trailer portion is left disconnected or ruptures, no trailer braking occurs until the tractor system pressure drops to a low level, resulting in long vehicle stopping distances and poor vehicle stability due to tractor braking without trailer braking. Furthermore, once the prior art trailer emergency brakes are applied, they cannot be easily released.